1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus which have the electrophotographic photosensitive member.
2. Related Background Art
Electrophotographic photosensitive members used in electrophotographic apparatus are required to have a stated sensitivity, electrical properties and optical properties which have been adapted to any electrophotographic process. In particular, the surface layers of electrophotographic photosensitive members are required to have durability to electrical and mechanical external forces because such forces are directly applied thereto through charging, development by toner, transfer to transfer materials, cleaning to remove residual toner, and so forth. Stated specifically, they are required to have durability against scratches and wear which are due to friction and, especially when a charging method involving discharge, durability against chemical deterioration due to ozone, nitrogen oxides and the like which may remarkably be generated in an environment of high humidity. At the time of the cleaning to remove residual toner, they are further required to have properties such as surface slip properties, releasability and stain resistance because there are problems of the adhesion of toner to electrophotographic photosensitive member surface and the blade turn-over when blade cleaning is performed.
To meet such requirements, it is proposed to use, as materials for the surface layers of electrophotographic photosensitive members, resins having good releasability and slip properties as typified by fluorine-atom-containing resins and resin materials having high hardness as typified by silicone resins, urethane resins and unsaturated ester materials.
However, any materials that may satisfy such various properties have not still been discovered. For example, the fluorine-atom-containing resins have a low hardness when used alone, and it is difficult for them to keep scratches from occurring. In addition, the fluorine-atom-containing resins are slightly soluble in solvents commonly used, and it is not easy for them to form films.
Japanese Patent Application Laid-open No. 61-072257 discloses an example in which a high-hardness material such as a curable silicone resin that utilizes the high reactivity of an alkoxysilane is used in an electrophotographic photosensitive member. Such a high-hardness material, however, has not been satisfactory in respect of slip properties, electrical properties in an environment of high humidity, and releasability. In addition, such a high-hardness material has a high reactivity with hydroxyl groups, and hence has restrictions on solvents when photosensitive layers are formed by coating. The curing reaction may also slowly proceed under the influence of water content, and hence coating fluids therefor may have a poor stability. Thus, there has been a problem also in respect of the productivity of electrophotographic photosensitive members.
A material which forms cured films utilizing the cleavage of unsaturated bonds as in prepolymers of diallyl phthalate resins, disclosed in Japanese Patent Application Laid-open No. 62-014657, is also commonly radically polymerizable. Coating fluids making use of this material are relatively stable to water content. However, only cured products having unstable electric properties in respect of insulation resistance and the like are obtainable because of, e.g., any faulty curing at film surface that is due to a polymerization inhibitory effect caused by oxygen in the air and any reaction to cut carbon-carbon bonds that is due to irradiation by light when a photoinitiator is used. Hence, this has brought about a problem that the transfer efficiency may lower because of a rise of surface energy of the electrophotographic photosensitive member or that images may blur as a result of moisture absorption.
Meanwhile, as materials used in the surface layers of electrophotographic photosensitive members, not only external properties such as the above hardness, rubbing-friction resistance and slip properties, but also internal electrical properties are required that do not make the movement of electric charges stagnate also in the interior of the surface layer. Where the surface layer of an electrophotographic photosensitive member has no function to move electric charges, the electric charges may accumulate in the interior of the photosensitive layer, and the repetition of the electrophotographic process of charging and exposure causes a rise of residual potential, resulting in a lowering of the quality level of images reproduced.
To solve this problem, a method is proposed in which a charge-transporting material is incorporated in the surface layer. However, when, e.g., a charge-transporting material is added to an alkoxysilane to effect curing, the siloxane component of the alkoxysilane has poor compatibility with the charge-transporting material in many cases. Also, when a charge-transporting material is incorporated in a resin containing a unit having a high polarity as in urethane resin, the mobility of electric charges in virtue of the charge-transporting material may lower, and any satisfactory electrophotographic performance can not be obtained. These are the actual circumstances.
Moreover, some thermosetting resins are not sufficiently curable when only subjected to heat treatment, and require addition of curing catalysts such as curing accelerators and polymerization initiators. Such materials are seen in variety. However, where such curing catalysts have remained in cured films, there is a possibility of causing a difficulty such that they inhibit the movement of electric charges even in a very small quantity or that the cured films have a low electrical resistance.
Coating fluids to which such curing catalysts have been added also have a tendency that the reaction may gradually proceed even at normal temperature, resulting in a poor coating fluid stability, and also causing a difficulty that it is difficult to produce and store coating fluids in a large quantity.
Japanese Patent Application Laid-open No. 10-228126 and so forth also disclose examples in which a charge-transporting material having a hydroxyphenyl group or a hydroxyalkyl group is incorporated in the surface layer of an electrophotographic photosensitive member. However, in such an electrophotographic photosensitive member as well, it is the actual circumstances that the requirements for higher durability, higher productivity and higher image quality in recent years have not been met and all the respects of mechanical strength, residual potential, productivity and so forth have not been made sufficiently satisfactory.